Brain Computer Interface (BCI) systems can provide an alternative way of communication and control for people with severe motor disabilities by allowing the human brain to control a computer directly without relying on normal neuromuscular pathways. The most important application for the BCI system is in the area of providing communication, control or rehabilitation tools for paralyzed people who are suffering from severe neuromuscular disorders so as to help compensate for or restore their lost abilities. For example, non-invasive, EEG-based BCI systems measure specific components of EEG activities, extract features from these components and translate these features into control signals to operate devices such as a cursor or a robot arm. Furthermore, BCI systems are also able to provide an important test-bed for the development of mathematical methods and multi-channel signal processing to derive command signals from brain activities.
A feature of brain signals that can be used in BCI systems is the evoke-related potential (ERP) for example, the P300 signal. The P300 signal is an endogenous, positive polarity component of the evoke-related potential (ERP) elicited in the brain in response to infrequent/oddball auditory, visual or somatosensory stimuli in a stream of frequent stimuli. It occurs at a latency of 300-600 ms after a target “oddball” stimulus and has a parietal distribution on the scalp. Furthermore, the amplitude of the P300 signal varies directly with the relevance of the eliciting events and inversely with the probability of the stimuli (or the inter-stimulus interval). On the other hand, exogenous factors such as stimulus size, stimulus duration and eccentricity do not usually give rise to significant changes in the P300 signal waveform. Coupled with the fact that almost all humans generate the P300 signal in response to infrequent/oddball stimuli, the stability of the P300 signal waveform in the presence of exogenous factors allows the P300 signal to be effectively used in BCI systems.
Traditional BCI systems, including P300-based BCI systems, work in a synchronous mode with the assumption that the user is always in the control state.
Therefore the BCI system is continuously translating concurrent brain signals to certain control commands even when the user does not intend to do so. This results in several false interpretations of the brain signals which in turn results in several responses of the BCI system not in accordance with the user's intent. Embodiments of the present invention seek to address one or more of the above problems.